A number of machines involved in mining, construction and public works use rolls that are driven for the crushing, mining, milling and the like of earthen materials. These earth working rolls include an array of tips to engage the material to be worked. The tips are releasably secured to holders attached to the roll at various locations. The tips are wear parts that are replaced after a certain length of use.
As one example, earth working tips can be provided in a roll crusher for the crushing of earthen material in a mining operation. In a typical operation (FIG. 53), the mined material 1 is dumped into a chute 3 and directed onto a conveyor 5 for transport to a roll crusher 7. The roll crusher 7 is a double roll crusher, which includes a pair of opposed rolls 9 to break up the mined material 1. Each roll 9 is fitted with an array of tips 11 adapted to engage the mined material and break it up (FIG. 54). The tips are secured to holders 13 that are fixed to the rolls 9. The rolls 9 are rotated in opposite directions so that the tips 11 are driven toward each other from the top. The broken material 1A passing through the roll crusher 7 is deposited on a second conveyor 17 for transport to rotary screens 19 for separation of the material.
Tip 11 is a one-piece member that includes a mounting shaft 21 for attachment to a holder 13, and a cone 23 for engaging the mined material 1 (FIGS. 55-57). Cone 23 has a conical exterior 25 with a rounded front end 27 corresponding to a generally spherical segment. The driving of the cone through the material in a conventional tip 11 imposes a substantial drag on the rotation of the roll as the earthen material drags along a full one half of the cone's large periphery. The use of many cones on a roll multiplies the drag such that high power requirement are needed to drive the rolls.
Mounting shaft 21 has a stepped configuration for a mating fit into a hole in holder 13, and a securing groove 31 into which the free end of a screw threaded into the holder is received to permit rotation of the cone during use. On account of the shape of the cones and its intended rotation, hardfacing 29 is applied over the entire cone 23. A double layer of hardfacing is applied over the leading portion 23A of the cone to extend the usable life of the tip. Hardfacing, however, is expensive and adds considerably to the overall cost of the tip.
The tip's shaft and the wall of the hole in the holder receiving the shaft are machined and close fitting to provide sufficient support for the tip. Even so, due to the invasiveness of earthen fines and the chaotic nature of a crushing or mining operation, fines commonly get embedded in the hole around the shaft. These fines tend to restrict and oftentimes prevent the rotation that is intended for the tip, thus, nullifying the potential gain of even wearing. Moreover, the presence of fines in the holder around the shaft can make the tip difficult to remove from the holder.